Safety in medical equipment starts with the supply of power

Paul Boughton

Electrical equipment used in medical technology must fulfil high requirements in terms of safety. This protects both the patient and medical staff. The protection begins with the safe supply of electric power.

SCHURTER offers a wide range of power sockets and power entry modules with and without power-line filters as well as filters for use in a broad range of equipment. These products fulfill the requirements of the base standard for medical electrical equipment, IEC/UL 60601-1 and can generally be used in most equipment without additional testing.

It is recommended to include a mechanism to protect against any unintentional removal of plugs from the equipment’s power sockets. In addition to cord-retaining brackets, SCHURTER offers the V-Lock cord retaining solution. With V-Lock, the power socket is equipped with a notch that interlocks with a special latch on the connector on the power cord. The system prevents the cord from being pulled out of the socket unintentionally.

All medical electrical equipment should be equipped with a double-pole fuse holder that can only be opened up with the help of a tool. It must further be ensured that only authorised personnel can remove or replace fuses. For this, SCHURTER offers the 'Extra-Safe' fuse drawers.

The line switch at the power feed has an important function. Just as with fuse holders, it must be ensured that the equipment is completely disconnected from the power network after being turned off. If only one pole in a non-polarised power distribution network is interrupted, the equipment could still be live. Thus, it is preferable to use a switch that disconnects the power feed on two poles.
The power-line filter protects the equipment from external HF interference and reduces the HF interference radiated by the equipment. Y capacitors wired between the power supply lines and earth within the power-line filter produce a leakage current to earth. This fault current can trigger the fault interrupter whereby the power supply is shut off. Thus, touch leakage current for medical electrical equipment may not exceed 100µA, and for devices with direct patient contact, it even drops down to 10µA. As a result, power-line filters for medical electric equipment do not have any Y capacitors, which results in a maximum leakage current of 5µA, or they have only very small Y capacitors such as of 470pF, which results in a peak leakage current of 80 µA.
If you pull a power cable out of a power socket, the stored voltage from the X capacitors is still present on the power pins. If touched, they can result in an electrical shock. Thus, medical electrical equipment with detachable power connectors may only have a maximum of 60V on the touchable plug pins one second after the plug has been pulled. To achieve this, a bleeder resistor is switched in between the phase and neutral conductors, and it discharges the capacitor in a very short time.